Transmission power control method of base station in ofdma-based wireless communication system

ABSTRACT

A power control method of a base station in a wireless communication system based on Orthogonal Frequency Division Multiple Access (OFDMA) is provided for reducing power consumption by turning off the bias of the power amplifier for the duration of a symbol carrying no user data. The method includes checking scheduling information of radio resources, detecting a symbol carrying no user data, based on the scheduling information, and turning off a bias of the power amplifier for a symbol duration of the symbol carrying no user data. The transmission power control method is capable of reducing power consumption of the base station by turning off the bias of the power amplifier of the base station for the symbol duration in which no user data is transmitted.

PRIORITY

This application is a divisional application of prior application Ser.No. 13/158,788, filed on Jun. 13, 2011, which claims the benefit under35 U.S.C. § 119(a) of Korean patent applications filed on Aug. 20, 2010,in the Korean Intellectual Property Office and assigned Serial No.10-2010-0080772, and on Nov. 9, 2010, in the Korean IntellectualProperty Office and assigned Serial No. 10-2010-0110855, the entiredisclosures of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to wireless communications. Moreparticularly, the present invention relates to a method and apparatusfor controlling power consumption of a power amplifier in a wirelesscommunication system.

2. Description of the Related Art

Mobile communication services have evolved in recent years from basicvoice communication services to advanced data communication servicesbased on the high speed wireless communication technologies such asWorldwide Interoperability for Microwave Access (WiMAX) and Long TermEvolution (LTE). These high speed wireless communication technologiesadopt OFDMA as a multiple access scheme.

In order to transmit large amounts of multimedia data in a high mobilityenvironment, there is a need for a power amplifier that is capable ofsupporting an increased bandwidth of modulation signals and a highpeak-to-average-power ratio. Owing to the characteristics of the datacommunication, the data traffic amount is likely to fluctuate abruptlyaccording to the user's service access time and types of services.

In the meantime, there has been discussion of a Green Base TransceiverStation (BTS) and low power base station with the concern of globalwarming. Key concerns of the discussion are to improve the energyefficiency of a Radio Frequency (RF) power amplifier which consumes over50% of the power of the base station, and the system optimization forrapid variation of data traffic.

There is therefore a need to develop a method for controlling the powerconsumption of the RF power amplifier of a base station.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide a transmission power control method andapparatus for the power amplifier of a base station that is capable ofminimizing power consumption by controlling the power amplifier tooperate in a maximum efficiency area when the Radio Frequency (RF)output power is changed according to the user data amount.

Another aspect of the present invention is to provide a transmissionpower control method and apparatus for the power amplifier of a basestation that is capable of reducing power consumption by controlling thepower on/off of the power amplifier according to the data trafficamount.

Yet another aspect of the present invention is to provide an interfacefor transferring user data allocation information from a digital unit toan RF unit.

In accordance with an aspect of the present invention, a method forcontrolling a power amplifier of a base station in a wirelesscommunication system based on Orthogonal Frequency Division MultipleAccess (OFDMA) is provided. The method includes checking schedulinginformation of radio resources, detecting a symbol carrying no user databased on the scheduling information, and turning off a bias of the poweramplifier for a symbol duration of the symbol carrying no user data.

In accordance with another aspect of the present invention, a basestation for a wireless communication system based on OFDMA is provided.The system includes a controller for acquiring information of a symbolcarrying no user data by referencing scheduling information of radioresources, and an RF unit for turning off a bias applied to a poweramplifier for a symbol duration of the symbol carrying no user data byreferencing the symbol information provided by the controller.

In accordance with still another aspect of the present invention, a basestation for a wireless communication system based on OFDMA is provided.The system includes a controller including a scheduler for assigningradio resources, and an RF unit acquiring information on a symbolcarrying no user data based on transmission powers of individual symbolswithin a frame and for turning off a bias applied to a power amplifierfor a symbol duration of the symbol carrying no user data.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a graph illustrating on/off timing of the bias applied to thepower amplifier of a base station in a Worldwide Interoperability forMicrowave Access (WiMAX) system according to an exemplary embodiment ofthe present invention;

FIG. 2A is a block diagram illustrating a configuration of a basestation according to an exemplary embodiment of the present invention;

FIG. 2B is a block diagram illustrating a configuration of an interfacefor transferring symbol information from a controller to an RF unit in abase station according to an exemplary embodiment of the presentinvention;

FIG. 3 is a diagram illustrating an information structure of a downlinksubframe transferred to a DU-RU connector through a first interface unitaccording to an exemplary embodiment of the present invention;

FIG. 4 is a diagram illustrating a structure of a first CPRI basic framein downlink subframe starts according to an exemplary embodiment of thepresent invention;

FIG. 5 is a flowchart illustrating a transmission power control methodof a base station according to an exemplary embodiment of the presentinvention;

FIG. 6 is a block diagram illustrating a configuration of a base stationaccording to an exemplary embodiment of the present invention;

FIG. 7 is a flowchart illustrating a transmission power control methodof a base station according to an exemplary embodiment of the presentinvention; and

FIG. 8 is a graph illustrating an on/off timing of the bias applied tothe power amplifier of a base station in a wireless communication systemaccording to an exemplary embodiment of the present invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the present invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

In the following, methods for controlling the power amplifier of a basestation are described with two exemplary embodiments. In the firstexemplary embodiment, a controller sends the information of the symbolcarrying no data to the Radio Frequency (RF) unit such that the RF unitcontrols an on/off state of the power amplifier. In the second exemplaryembodiment, the RF unit detects the symbol carrying no user datadirectly and controls the on/off state of the power amplifier based onwhether it is detected that a symbol carries user data. The firstexemplary embodiment also includes a method for providing an interfacefor transferring the symbol information from a Digital Unit (DU)(controller) to the RF unit.

In the Orthogonal Frequency Division Multiple Access (OFDMA) system, thecontrol and data channels are assigned subcarriers in frequency domainand symbols in time domain. How to map the subcarriers and symbols tothe control and data channels assigned to the mobile terminals isdetermined according to the type of the system and technical standard ofthe system. In an exemplary case of a Long Term Evolution (LTE) Advanced(LTE-A) system, a Resource Block (RB) is defined as 12 consecutivesubcarriers in the frequency domain and 14 symbols in the time domain.

When mapping the user data to the RF resource assigned to the terminal,it is considered preferable to perform resource mapping in the frequencydomain. In this frequency domain-preferred resource mapping scheme, theuser data mapping is performed first in a symbol across entire systembandwidth and then in the next symbol. In the case of using thefrequency domain-preferred resource mapping scheme, there can be symbolscarrying the pilot signal but no user data. Since the pilot symbolscarry no user data, it is possible to turn off the bias of the poweramplifier during the pilot symbols.

FIG. 1 is a graph illustrating on/off timing of the bias applied to thepower amplifier of a base station in a Worldwide Interoperability forMicrowave Access (WiMAX) system according to an exemplary embodiment ofthe present invention. In FIG. 1, the y-axis denotes the amplitude of asignal, and the x-axis denotes time.

Referring to FIG. 1, the time axis is divided into Period A, Period B,and Period C. In Period A, the data signal and pilot signal are carriedsimultaneously, while only the pilot signal is carried in Period B, andno signal is carried in Period C. Of course, it is possible that nosignal is carried in Period B according to scheduling informationalthough the power amplifier is on.

In the conventional WiMAX system, the bias of the power amplifier isalways on without taking into consideration the differences of thePeriods A, B, and C. However, there is no need to turn on the bias forthe Period B during which no data signal is transmitted. In an exemplaryembodiment of the present invention, the base station controls to turnoff the bias of the power amplifier for the Period B so as to reduce thepower consumption of the base station.

A description is made of a method for controlling the power amplifier ofa base station in exemplary embodiments hereinafter.

First Exemplary Embodiment

In an exemplary embodiment of the present invention, a controller sendsthe information of the symbol carrying no user data to an RF unit suchthat the RF unit controls an on/off state of the power amplifier basedon the information.

FIG. 2A is a block diagram illustrating a configuration of a basestation according to an exemplary embodiment of the present invention.

Referring to FIG. 2A, the base station according to this exemplaryembodiment includes a controller 210 including a scheduler 220 having asymbol location indicator 230 and a modem 235, a memory 215, and an RFunit 240 including a frame synchronization detector 250, a symbollocation detector 260, a bias controller 270, and a power amplifier 280.

The controller 210 controls operations of the base station for providingmobile communication services to the end user terminals. In an exemplaryembodiment of the present invention, the controller 210 can be called aDigital Unit to distinguish it from the RF unit 240 responsible for theradio communication function. More particularly, in an exemplaryembodiment of the present invention, the controller 210 can controlsignaling among the internal function blocks such that the bias of thepower amplifier is turned off for the duration of the symbol carrying nouser data. The controller 210 can further include the modem 235 and thescheduler 220 having the symbol location indicator 230.

The scheduler 220 performs scheduling on the control signals and userdata to be transmitted to end user terminals. According to an exemplaryembodiment of the present invention, the scheduler 220 performs resourcescheduling in a symbol across the entire system bandwidth first, andthen in the next symbol. By assigning resources in this manner, therecan be at least one symbol carrying no user data.

The symbol location indicator 230 outputs non-data symbol indicationinformation generated based on the resource assignment informationprovided by the scheduler 220. The non-data symbol indicationinformation can include the symbol location information (e.g., the startpoint of the non-data symbol) and/or a number of non-data symbols, butis not limited to this kind of information. In an exemplary embodimentof the present invention that is described hereinafter, the symbolinformation can be defined as the information on the symbol to which nouser data is mapped in each frame. The symbol information can be, forexample, the location information (i.e., start point) on the symbol towhich no user data is mapped or a number of the symbols, but is notlimited thereto.

According to an exemplary embodiment of the present invention, thescheduler 220 can store the information on the symbol temporarily.

Although the description is directed to the case where the symbollocation indicator 230 acquires the information on the symbol carryingno user data, the present invention is not limited thereto. According toan exemplary embodiment of the present invention, the symbol locationindicator 230 can be configured to acquire the information about atleast one of the symbol carrying user data and the symbol carrying nouser data. That is, the symbol location indicator 230 can output thesymbol information about both the symbols carrying the user data andsymbols carrying no data.

Since both the scheduler 220 and the symbol location indicator 230 inthis exemplary embodiment are integrated into the controller 210, thesymbol location indicator 230 can acquire the scheduling information,i.e., resource assignment information, from the scheduler 220 directly.The symbol location indicator 230 sends the symbol information to themodem.

The modem 235 outputs the symbol of the baseband signal generated usinga predetermined modulation and coding scheme based on the resourceallocation information of the scheduler 220. Simultaneously, the modem235 acquires the information on the symbol to which no user data ismapped and sends this information to the RF unit 240. The interface fortransferring the symbol information from the modem 235 to the RF unit240 is described later.

The RF unit 240 is responsible for processing radio signals carrying thecontrol signal and user data transmitted to the terminals. Although notdepicted in drawing, the RF unit 240 can include an RF transmitter forup-converting and amplifying transmission signals and an RF receiver forlow-noise-amplifying and down-converting received signals. In FIG. 2A,only the part of the RF transmitter (Tx) is depicted. The RF unit 240can receive the control signal and data over a radio channel, and canoutput the control signal and data to the controller and transmit thedata input from the controller 210 over the radio channel.

In an exemplary embodiment of the present invention, the RF unit 240,particularly RF transmitter, includes the frame synchronization detector250, the symbol location detector 260, the bias controller 270, and thepower amplifier 280.

The frame synchronization detector 250 is responsible for acquiringframe synchronization and symbol synchronization.

The symbol location detector 260 detects the symbol carrying no userdata in every frame to be transmitted on the basis of the symbolinformation provided by the controller 210. The symbol location detector260 can also calculate the length (or duration) of the symbol carryinguser data, based on the symbol information, and transfer the symbollength information to the bias controller 270.

Although the description is directed to the exemplary case where thesymbol location detector 260 detects the location of the symbol carryingno user data and calculates the length of the symbol carrying the userdata, the present invention is not limited thereto, but can beimplemented in other embodiments with or without modifications.

According to an exemplary embodiment of the present invention, thesymbol location detector 260 can be configured to detect at least one ofthe symbol carrying the user data and the symbol carrying no user data,and to calculate the length of each symbol.

The bias controller 270 receives the symbol length information of thesymbol carrying the user data from the symbol location detector 260. Thebias controller 270 can control an on/off state of the bias applied tothe power amplifier 280 based on the symbol length information. In moredetail, the bias controller 270 issues an ON control signal to the poweramplifier 280 to power on for the symbol duration of the symbol carryinguser data. Meanwhile, the bias controller 270 issues an OFF controlsignal to the power amplifier 280 to power off for the symbol durationof the symbol carrying no user data.

The power amplifier 280 amplifies the power of the signal (symbol) to betransmitted to the mobile terminal. More particularly, in an exemplaryembodiment of the present invention, the power amplifier 280 powers onfor the symbol duration of the symbol carrying user data to transmit thepower-amplified signal under the control of the bias controller 270.Meanwhile, the power amplifier 280 powers off for the symbol duration ofthe symbol carrying no user data, resulting in no transmission.

FIG. 2B is a block diagram illustrating a configuration of an interfacefor transferring symbol information from a controller to an RF unit in abase station according to an exemplary embodiment of the presentinvention.

In the following description, the internal interface of the basestation, and more particularly the interface connecting the controller210 and the RF unit 240, follows the Common Public Radio Interface(CPRI), but is not limited thereto.

Referring to FIG. 2B, the modem 235 includes a first interface unit 236for transferring the symbol information. The modem 235 converts thesymbol information acquired from the memory 215 to the downlink subframeinformation (which is described later) and transfers the downlinksubframe information to the DU-RF Unit (RU) connection unit 245 via thefirst interface unit 236. According to an exemplary embodiment of thepresent invention, the first and second interface units 236 and 237connected with each other are the Automatic Data Interface Bus Interface(ADI BUS).

In this case, the downlink subframe information transferred to the DU-RUconnection unit 245 via the first interface unit 236 can be structuredas shown in FIG. 3.

FIG. 3 is a diagram illustrating an information structure of a downlinksubframe transferred to a DU-RU connector through a first interface unitaccording to an exemplary embodiment of the present invention

Referring to FIG. 3, the downlink subframe information includes acontrol information region 310 indicating a start point of a downlinksubframe and a data sample region 320. In this case, the four bits of b0to b1 of the period P0 are set to ‘1111’ as the start indicatorindicating the start of the downlink subframe. Also, the eight bits ofp8 to p15 of the period P0 are reserved for future use. In an exemplaryembodiment of the present invention, the reserved eight bits of b8 tob15 of the period P0 as the first control signal of the control region310 are used for the symbol information.

In the case of the Word Interoperability for Microwave Access (WiMAX)system based on the Institute of Electrical and Electronics Engineers(IEEE) 802.16e, the maximum number of the OFDM symbols constituting adownlink subframe is 35, although this varies depending on the TimeDivision Duplex (TDD) Symbol Ratio, and this means that the eight bitsare enough to indicate the symbol information.

The DU-RU connection unit 245 establishes a connection between thecontroller 210 and the RF unit 240 and transfers the symbol informationto the RF unit 240. For this purpose, the DU-RU unit 245 includes asecond interface unit 237, a conversion unit 238, and a third interfaceunit 239.

The second interface unit 237 transfers the downlink subframeinformation received from the first interface unit 236 to the conversionunit 238.

The conversion unit 238 analyzes the received downlink subframeinformation to extract the symbol information and data sample. Theconversion unit 238 also converts the extracted symbol information anddata sample to the Basic Frame information according to the CPRIprotocol. In a case of using 10 MHz channel bandwidth and dual stream 2Transmit 2 Receive (2T2R), 35 WiMAX sample IQ data are transmitted in 12CPRI basic frames. Particularly in the first CPRI basic frame in whichthe downlink subframe starts as shown in FIG. 4, only ‘bit15:8’ amongthe last 16 bits are used as the current downlink/uplink startindicator. Accordingly, the conversion unit 238 according to anexemplary embodiment of the present invention transmits the symbolinformation using 8 bits of ‘bit7:0’ which is not used among the last 16bits of the first basic frame in which the downlink subframe starts.

The third interface unit 239 receives the basic frame information fromthe conversion unit 238 and outputs the basic frame information to thefourth interface unit 255. According to an exemplary embodiment of thepresent invention, the third and fourth interface units 239 and 255 canbe the CPRI InterFaces (CPRI I/F).

The fourth interface unit 255 receives the basic frame from the thirdinterface unit 239 and outputs the basic frame to the symbol locationdetector 260.

The symbol location detector 260 extracts the symbol information fromthe basic frame. Next, the symbol location detector 260 detectslocations of the symbols to which no user data are mapped in each frameand executes the subsequent process.

FIG. 5 is a flowchart illustrating a transmission power control methodof a base station according to an exemplary embodiment of the presentinvention.

Referring to FIG. 5, the scheduler 220 performs resource assignment toend user terminals for transmitting the control signals and user data tothe terminals in step S510. According to an exemplary embodiment of thepresent invention, the radio resource assignment process is performedsuch that the frequency resource is first assigned in a symbolcompletely, and then in the next symbol.

Next, the symbol location indicator 230 detects the location of thesymbol carrying no user data in every frame in step S520. The symbollocation indicator 230 sends the information on the detected symbol tothe RF unit 240 in step S530. The symbol information can includelocation of the symbol carrying no user data and/or a number of symbolscarrying no user data.

The frame synchronization detector 250 of the RF unit 240 acquires framesynchronization and symbol synchronization with the end user terminal instep S540. Next, the symbol location detector 260 detects the locationof the symbol carrying no user data in every frame on the basis of thesymbol information provided by the symbol location indicator 230 in stepS550. At this time, the symbol location detector 260 also calculates thesymbol duration (i.e., the symbol length) of the symbol carrying userdata.

Next, the bias controller 270 determines a bias-on period for turning onthe bias and a bias-off period for turning off the bias, on the basis ofthe information about the symbol carrying user data, in step S560. Here,the bias-on period is the period during which the user data istransmitted to the terminal, and the bias-off period is the periodduring which no user data is transmitted to the terminal.

Finally, the bias controller 270 controls the bias applied to the poweramplifier, to be turned on for the bias-on period and off for thebias-off period, in step S570.

As aforementioned, the bias applied to the power amplifier is turned offfor the symbol duration in which no user data is transmitted, resultingin reduction of power consumption of the power amplifier of a basestation.

Second Exemplary Embodiment

In an exemplary embodiment of the present invention, the RF unit detectsthe symbol carrying no user data and controls the on/off state of thepower amplifier based on the detection result.

FIG. 6 is a block diagram illustrating a configuration of a base stationaccording to an exemplary embodiment of the present invention.

Referring to FIG. 6, the base station includes a controller 610including a scheduler 620, and an RF unit 630 including a framesynchronization detector 640, a symbol power detector 650, a symbollocation detector 660, a bias controller 670, and a power amplifier 680.

The controller 610 controls entire operations of the base station forproviding mobile communication services to the end user terminals. Asdescribed in the exemplary embodiment above, the controller 610 cancontrol signaling among the internal function blocks such that the biasof the power amplifier is turned off for the duration of the symbolcarrying no user data. The controller 610 can further include thescheduler 620.

The scheduler 620 performs scheduling on the control signals and userdata to be transmitted to the terminals. According to an exemplaryembodiment of the present invention, the scheduler 620 performs resourcescheduling in a symbol across the entire system bandwidth first, andthen in the next symbol.

In an exemplary embodiment of the present invention, the controller 610is basically identical with that of the exemplary embodiment describedabove except that the controller 610 has no function block for acquiringinformation about the symbol carrying no user data. According to thisexemplary embodiment of the present invention, the RF unit 630 acquiresthe information on the symbol carrying no user data directly.

The RF unit 630 is responsible for processing radio signals carrying thecontrol signal and user data transmitted to the terminals. Although notdepicted in the drawing, the RF unit 630 can include an RF transmitterfor up-converting and amplifying transmission signals and an RF receiverfor low-noise-amplifying and down-converting received signals. In FIG.6, only the part of the RF transmitter (Tx) is depicted. The RF unit 630can receive the control signal and data over a radio channel, and canoutput the control signal and data to the controller and transmit thedata input from the controller 610 over the radio channel.

In an exemplary embodiment of the present invention, the RF unit 630 caninclude the frame synchronization detector 640, the symbol powerdetector 650, the symbol location detector 660, the bias controller 670,and the power amplifier 680.

The frame synchronization detector 640 is responsible for acquiringframe synchronization and symbol synchronization.

The symbol power detector 650 detects the transmission powers ofindividual symbols in a frame. The symbol power detector 650 alsoacquires the information of the symbol carrying no user data based onthe transmission power of the symbol. The symbol information can containthe location information about the symbol carrying no user data and/or anumber of symbols carrying no user data.

The symbol location detector 660 detects the symbol carrying no userdata in every frame to be transmitted on the basis of the symbolinformation provided by the symbol power detector 650. The symbollocation detector 660 can also calculate the length (or duration) of thesymbol carrying user data based on the symbol information, and transferthe symbol length information to the bias controller 670.

As described above in an exemplary embodiment of the present invention,the bias controller 670 receives the symbol length information of thesymbol carrying the user data from the symbol location detector 660. Thebias controller 670 can control an on/off state of the bias applied tothe power amplifier 680 based on the symbol length information. In moredetail, the bias controller 670 issues an ON control signal to the poweramplifier 680 to power on for the symbol duration of the symbol carryinguser data. Meanwhile, the bias controller 670 issues an OFF controlsignal to the power amplifier 680 to power off for the symbol durationof the symbol carrying no user data.

As described above in an exemplary embodiment of the present invention,the power amplifier 680 amplifies the power of the signal (symbol) to betransmitted to the mobile terminal. More particularly, in an exemplaryembodiment of the present invention, the power amplifier 680 powers onfor the symbol duration of the symbol carrying user data to transmit thepower-amplified signal under the control of the bias controller 670.Meanwhile, the power amplifier 680 powers off for the symbol duration ofthe symbol carrying no user data, resulting in no transmission.

FIG. 7 is a flowchart illustrating a transmission power control methodof a base station according to an exemplary embodiment of the presentinvention.

Referring to FIG. 7, the scheduler 620 performs resource assignment toend user terminals for transmitting the control signals and user data tothe terminals in step S710. According to an exemplary embodiment of thepresent invention, the radio resource assignment process is performedsuch that the frequency resource is assigned in a symbol completely andthen in the next symbol.

Next, the frame synchronization detector 640 of the RF unit 630 acquiresframe synchronization and symbol synchronization with the terminal instep S720. After acquiring frame and symbol synchronizations, the symbolpower detector 650 detects the transmission powers of the individualsymbols in a frame in step S730. The symbol power detector 650 canacquire the information on the symbol carrying no user data based on thedetected transmission power of each symbol, and outputs the acquiredsymbol information.

The symbol location indicator 660 detects the location of the symbolcarrying no user data in every frame based on the symbol informationprovided by the symbol power detector 650 in step S740. The symbollocation detector 660 also calculates the duration (i.e., the symbollength) of the symbol carrying user data in step S750.

Next, the bias controller 670 determines a bias-on period for turning onthe bias and a bias-off period for turning off the bias on the basis ofthe information about the symbol carrying user data in step S760. Here,the bias-on period is the period during which the user data istransmitted to the terminal, and the bias-off period is the periodduring which no user data is transmitted to the terminal.

Finally, the bias controller 670 controls the bias applied to the poweramplifier to be turned on for the bias-on period and off for thebias-off period in step S770.

FIG. 8 is a graph illustrating on/off timing of the bias applied to thepower amplifier of a base station in a wireless communication systemaccording to an exemplary embodiment of the present invention.

Referring to FIG. 8, the y-axis denotes the amplitude of a signal, andthe x-axis denotes time. The time axis is divided into Period A, PeriodB, and Period C. In Period A, the data signal and pilot signal arecarried simultaneously, while only the pilot signal is carried in PeriodB, and no signal is carried in Period C.

As shown in FIG. 8, the bias applied to the power amplifier turns offfor the Period B in which only the pilot signal is transmitted. Thismeans that the power control method of the present invention is capableof increasing the turn-off period of the power amplifier, resulting in areduction of the power consumption of the power amplifier of a basestation.

Table 1 shows the power saving effects in the WiMAX system using 29symbols per frame with the power control method according to anexemplary embodiment of the present invention.

TABLE 1 Case Power saving 25 symbols: bias on 25 symbols: bias offImprovement of 4.7% in comparison to bias on 21 symbols: bias on 21symbols: bias off Improvement of 12.5% in comparison to bias on 19symbols: bias on 19 symbols: bias off Improvement of 15.2% in comparisonto bias on 17 symbols: bias on 17 symbols: bias off Improvement of 19.3%in comparison to bias on

Referring to the first case of Table 1, assuming a WiMAX system using 29symbols (25 carrying user data and 4 carrying no user data), the bias ofthe power amplifier is turned on for the 25 symbols carrying user dataand off for the 4 symbols carrying no user data, and this results in thepower-saving effect of 4.7% as compare to the case where the bias of thepower amplifier is turned on for all of the 29 symbols. Greaterimprovements of 12.5%, 15.2%, and 19.3% power savings were measured whenthe number of test symbols carrying user data was reduced to 21, 19, and17, respectively.

As described above, the transmission power control method of a basestation according to the present invention is capable of reducing thepower consumption of the base station by turning off the bias of thepower amplifier of the base station for the symbol duration in which nouser data is transmitted.

While the present invention has been shown and described with referenceto certain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined in the appended claims and their equivalents.

What is claimed is:
 1. A base station in an Orthogonal FrequencyDivision Multiple Access (OFDMA) wireless communication system, the basestation comprising: a digital unit; and a Radio Frequency (RF) unitconfigured to: receive, from the digital unit, symbol informationregarding a symbol via a Common Public Radio Interface (CPRI), based onthe received symbol information, identify whether the symbol includesdata, and based on identifying that the symbol does not include data,control to turn off a bias of a power amplifier in a duration of thesymbol.
 2. The base station of claim 1, wherein the RF unit is furtherconfigured to control to turn on the bias of the power amplifier in theduration of a symbol based on identifying that the symbol includes data.3. The base station of claim 1, wherein the digital unit is furtherconfigured to generate the symbol information based on identificationresult of the symbol not including data.
 4. The base station of claim 1,wherein the symbol information includes at least one of: a position ofthe symbol respective to a sub-frame or a number of symbols notincluding data.
 5. The base station of claim 4, wherein the RF unit isfurther configured to determine a start time of turning-off of the biasof the power amplifier based on the position of the symbol.
 6. The basestation of claim 4, wherein the RF unit is further configured todetermine duration of turning-off of the bias of the power amplifierbased on the number of the symbols not including data.
 7. The basestation of claim 1, wherein the received symbol information is incontrol signal in a CPRI frame.
 8. The base station of claim 1, whereinthe digital unit is further configured to identify that the symbol doesnot include data based on schedule information provided by a schedulerincluded in the digital unit.
 9. The base station of claim 8, whereinthe schedule information includes resource assignment information andthe digital unit is further configured to identify that the symbol doesnot include data based on the resource assignment information.
 10. Thebase station of claim 1, wherein the symbol information includes bitinformation included in a specific position of a CPRI frame.
 11. Thebase station of claim 1, wherein the RF unit is further configured toreceive the symbol information regarding the symbol by identifying thesymbol information in a CPRI frame including the symbol information andI/Q data samples of the symbol.
 12. A method for controlling a poweramplifier of a base station in an Orthogonal Frequency Division MultipleAccess (OFDMA) wireless communication system, the method comprising:receiving, from a digital unit, symbol information regarding a symbolvia a Common Public Radio Interface (CPRI); based on the received symbolinformation, identifying, by a Radio Frequency (RF) unit, whether thesymbol includes data; and based on identifying that the symbol does notinclude data, controlling, by the RF unit, to turn off a bias of a poweramplifier in a duration of the symbol.
 13. The method of claim 12,further comprising: controlling to turn on the bias of the poweramplifier in the duration of a symbol based on identifying that thesymbol includes data.
 14. The method of claim 12, further comprising:generating, by the digital unit, the symbol information based onidentification result of the symbol not including data.
 15. The methodof claim 12, wherein the symbol information includes at least one of: aposition of the symbol respective to a sub-frame or a number of symbolsnot including data.
 16. The method of claim 15, further comprising:determining, by the RF unit, a start time of turning-off of the bias ofthe power amplifier based on the position of the symbol.
 17. The methodof claim 15, further comprising: determining, by the RF unit, durationof turning-off of the bias of the power amplifier based on the number ofthe symbols not including data.
 18. The method of claim 12, wherein thereceived symbol information is in control signal in a CPRI frame. 19.The method of claim 12, further comprising: identifying, by the digitalunit, that the symbol does not include data based on scheduleinformation provided by a scheduler included in the digital unit. 20.The method of claim 19, wherein the schedule information includesresource assignment information, and wherein the method furthercomprises identifying that the symbol does not include data based on theresource assignment information.